A common type of prior art window screen, usually having an aluminum frame, has a channel in the frame along all four sides of the screened area. Referring to Prior art illustrations in FIGS. 1, 4A and 4B, when a screen is framed to make an assembled window screen, screening material 20 is positioned with the edges extending across and a bit beyond the outside edge of the channel 28. Then a flexible, resilient “spline” 10 with a generally circular cross section is pressed down into the channel and it pushes the edge of the screening down in with it. Since the spline has a body diameter Wb that is comparable to, or slightly larger than, the width We of the channel, and is resilient, it will hold the screening in place by squeezing it between the spline and the inside wall(s) of the channel, thereby creating a frictional holding or gripping force to resist pull-out of the screening. This holding force needs to be of sufficient magnitude to hold the screening in tension across the frame so as to make it uniformly flat, not wavy or wrinkled or floppy. As seen in FIG. 1, the prior art spline 10 typically has short longitudinal ribs 14 spaced apart around the circumference of the spline's body. The ribs are formed along with the body (e.g., by extrusion) out of the same resilient material as the rest of the spline and they provide easily deformed resilient grippers. Since the ribs add to the nominal diameter of the spline body they add extra resilient spring-back pressure against the channel walls thereby increasing frictional resistance to the spline being pulled back upward and out of the channel. As shown, the body 12 may be hollow (center axial hole 16) for providing easier compressibility.
A problem with the prior art is that the spline is difficult to push down into the channel properly. It is long and squirmy, and cannot be longitudinally “rubbed” into place since the resilient material has a relatively high coefficient of friction. Furthermore, due to its flexibility, it is difficult to press into place in a way that provides a uniform tension on the screening at all points around the perimeter of the screen. This is most problematic if an inexperienced person is trying to press the spline into place by hand. This problem is reduced, but not eliminated, by using a special-purpose spline roller 62 installation tool. Like a “pizza-cutter”, the tool includes a rotatable wheel on a handle. On better quality tools the wheel may have a pulley-like groove around its circumference to help the user keep the tool on top of the round spline body. The tool is placed on the spline and is pushed downward and forward to force the spline into the channel a little bit at a time as it is rolled along the spline above the channel. Tension on the screening now depends upon the user being able to maintain a uniform and adequate downward force on the tool while also maintaining a uniform forward speed that is adequate to allow time for the spline to be pressed downward before moving on to the next incremental length portion of the spline. Also, if not advanced in line with the channel, then the wheel will roll off the top of the spline, thus interrupting a uniform installation, and often cutting the screen. The same problem occurs if the squirmy spline is not held in line with the channel. Furthermore, the diameter of the spline varies inversely with the amount of stretching force applied to it as the user pulls it out straight ahead of the installation tool. This, of course, further adds variability to the tension and gripping force of the installed spline 10.
A further problem with the prior art splines is that proper installation means that the spline should be pressed down into the channel below the surface of the frame. This can only be done by using a pushing tool, such as the pizza cutter style spline roller 62, that is narrower than the channel width Wc. Using such a tool requires carefully controlled pressure exerted by the installer in a direction carefully aligned with the channel, which is hard on the wrist, because otherwise the thin roller easily rolls off the round spline and can cut the screen.
Thus an object of the present invention is to overcome many of the above described deficiencies and limitations of the prior art splines, installation methods, and/or installation tools.